The mysteries of the deep have been revealed after a remarkable 10-year survey of the world’s oceans.

Altogether, the international Census of Marine Life counted 201,206 different species – of which 5,000 are new.

But experts estimate there are a million species living in the sea, so a mere 20% of the huge total have been discovered so far.

Dr Jesse Ausubel, co-founder of the census, told a celebration at the Royal Institution yesterday: “We have created a baseline of what lives in the ocean, where and when.

“There was chaos in the records when we set out. But there are decades of work ahead.”

Science committee chairman Dr Ian Poiner added: “This is a milestone for marine science. We have a benchmark which will serve scientists for years to come.”

More then 2,700 experts spent 9,000 days at sea on more than 540 expeditions, recording everything from microbes to whales.

Thirty-million observations of 120,000 species have been organised in the global marine life database, the Ocean Biogeographic Information System.

It will provide a record against which future changes in ocean life can be measured. The ­scientists found that fish make up 16,764 of the known species. But there are thought to be 21,800, with up to 150 new species discovered every year.

Pacific Bluefin tuna were found to cross the Pacific three times in 600 days.